1. Field of the Invention
The invention relates to a pipe bend, in particular for a siphon installation, formed by two pipe parts, the centre lines of which enclose an angle, and a curved pipe part connecting these parts, including means extending from the curved connecting part in one of the pipe parts for guiding a liquid flow in the pipe part. Such a pipe bend is known from e.g. EP-A-0 493 302 or GB-A-2 041 477.
2. Description of the Prior Art
The first mentioned prior art document EP-A-0 493 302 discloses a mechanism to reduce pressure losses in angled conduits for transporting liquids. These pressure losses result from two-dimensional boundary layer separation wich occurs immediately downstream of sharp turns in the conduit. In order to eliminate or decrease such separation the prior art document provides a convoluted surface on the inner corner surface of the pipe bend, which surface is defined by a number of ridges protruding form the inner corner surface into the pipe bend and extending parallel to the direction of flow of the liquid. These ridges and the throughs defined therebetween produce a flow variation which allows the boundary layer to re-attach to the inner surface quickly.
GB-A-2 041 477 discloses a fluid pipeline elbow having provisions for suppressing cavitation. These provision include a curved vane provided in this elbow and spanning the width of the pipeline from one sidewall to the other. This curved vane extends substantially parallel to the centreline of the pipeline elbow, but may have its upstream edge arranged at a slight angle to the centreline of the upstream portion of the pipe.
Both prior art documents discussed above are intended to guide a flow of liquid through a pipe bend with minimal disturbance, i.e. such that the flow closely follows the course of the pipe bend. Such pipe bends are not suitable for connecting a riser pipe and a fall pipe in a siphon installation as the smooth flow of liquid will not start siphoning action.
The design of a pipe bend for use in a siphon installation to connect a riser pipe and a fall pipe is of great importance for the response of a siphon installation. In fact the siphoning action begins when a liquid in the riser pipe has risen so far that it flows through the pipe bend to the fall pipe and there forms a liquid curtain which covers the whole cross-section of the fall pipe. An underpressure is in that case generated behind the liquid curtain, whereby liquid is drawn up out of the riser pipe, whereafter a new liquid curtain is formed which again generates an underpressure, and so on. In this manner liquid is siphoned out of the riser pipe to the fall pipe. A siphon installation operating according to this principle is described for instance in the European patent specification 0 011 778 and is applied particularly in systems for draining waste water from dwellings. The siphon installation is herein intended to guarantee a considerable flow speed in the pipe system, even in the case of relatively small quantities of waste water, whereby a good flushing action is obtained and the risk of deposition and blockage is reduced.
The importance of a good design of the siphon installation, and particularly of the pipe bend used therein, is increasing now that the water consumption per household is being pushed back ever further and the quantity of water available in the system for flushing is therefore becoming smaller. The invention therefore has for its object to provide an improved pipe bend which is distinguished from known pipebends in that said flow guiding means are arranged for forming, in use, a liquid curtain for starting a siphoning action. By thus guiding the liquid flow such that a liquid curtain is formed, the pipe part is closed off relatively quickly and an underpressure is created behind the liquid curtain, which is important for starting a siphoning action.